1. Field of the Invention
This invention relates to a pilot injection controller in an internal combustion fuel injection system and a method of controlling the quantity of pilot-injected fuel, more particularly to a pilot injection controller in a fuel injection system with a fixed pilot injection plunger delivery stroke wherein optimum quantity of pilot-injected fuel can be achieved over a wide range of engine speeds by controlling the plunger delivery velocity and to a method of controlling the quantity of pilot-injected fuel therewith.
2. Prior Art
Prior art engine fuel injection systems use a cam connected with the engine to reciprocate each plunger for delivering fuel to the associated combustion chamber. As taught by Japanese Patent Public Disclosure Sho 62-55436, for example, some fuel injection systems of this type reduce combustion noise and generation of oxides of nitrogen (NOx) by preceding the main fuel injection with a pilot fuel injection which injects a smaller quantity of fuel than the main fuel injection.
The desired quantity of pilot-injected fuel is, for example, generally about 5 mm.sup.3. In a fuel injection system in which the delivery stroke of the plunger for pilot injection has a fixed pilot injection delivery stroke, however, the quantity of pilot-injected fuel varies greatly with the speed of the engine or cam.
Specifically, the quantity of pilot-injected fuel in the low-speed region is zero or at any rate very small owing to the small delivery energy, while it becomes large in the high-speed region owing to the dynamic effect and/or the preflow effect, so that in extreme cases the pilot injection may continue into the main injection and make it impossible to achieve the purpose of the pilot injection.
In a fuel injection system in which the quantities of fuel injected in the main and pilot injections are both electronically controlled (as described in Japanese Patent Public Disclosure Hei 3-233142, for example), the quantity of pilot-injected fuel can be appropriately controlled by appropriately opening and closing a solenoid valve in response to the engine speed, cam speed and/or other operating conditions. On the negative side, however, the system becomes complex, large and expensive, while the desired rapid control cannot always be achieved in actual operation because of problems with the opening-closing response of the solenoid valve.
Although constituting a fuel injection system to enable mechanical instead of electronic control of the quantity of pilot-injected fuel would enable structural simplification and avoid cost increase, it would lead to problems particularly in the case of a fuel injection system of the type in which the fuel delivery stroke for pilot injection is fixed (cannot be varied at as desired). Specifically, since, as explained in the foregoing, the quantity of pilot-injected fuel varies with engine speed, it would become difficult to achieve a sufficient pilot injection quantity in the low speed region.
This invention was completed in the light of the foregoing problem and has as one object to provide a pilot injection controller in a fuel injection system which makes it possible to obtain a constant quantity of pilot-injected fuel over a wide range of engine speeds and a method of controlling the quantity of pilot-injected fuel therewith.
Another object of the invention is to provide a pilot injection controller in a fuel injection system which enables optimization of the quantity of pilot-injected fuel over a wide range in a fuel injection system of the type in which the fuel delivery stroke for pilot injection is fixed and a method of controlling the quantity of pilot-injected fuel therewith.
Another object of the invention is to provide a pilot injection controller in a fuel injection system which enables optimization of the quantity of pilot-injected fuel over a wide range by controlling the actual delivery velocity of a plunger to a fixed value and a method of controlling the quantity of pilot-injected fuel therewith.